Carbosiloxane dendrimer

Fig. 6.20 Small angle scattering intensity (triangles log I) and effective diffusion DgfKQ) obtained from g=A carbosiloxane dendrimers with perfluorinated end groups in perfluo-rohexane. The dashed line is a fit to the prediction of a model for shape fluctuations of micro-emulsion droplets, the resulting bending modulus was 0.5 k T. (Reprinted with permission from [308]. Copyright 2003 Springer Berlin Heidelberg New York)...

In order to illustrate the assembly of carbosiloxane dendrimers, the smallest core unit will first be considered. A fourth-generation cauliflower dendrimer (Fig. 4.46) was obtained via a repetitive synthetic sequence with the aid of di-chloromethylsilane as hydrosilylation and allyl alcohol as alcoholysis reagent... 

A cyclic core unit can also provide a foundation for carbosiloxane dendrimers (Table 4.4 and Fig. 4.47). The scaffold then shows a somewhat less compact geometry ( cyclic spacing ) in the core region - in contrast to the situation with linear spacing. 

Kim et al. employed a divergent-repetitive synthetic route (see above, carbosilane dendrimers) to obtain mixed carbosilane/carbosiloxane dendrimers... 

Carbosiloxane dendrimers with SiH end groups (Fig. 4.48) [92] are generally accessible by hydrosilylation of MeCOCH2CH2CH=CH2 with chlorosilanes to yield Si-Cl terminated compounds and subsequent reduction with lithium aluminium hydride to form the corresponding alcohol with terminal SiH groups. 

Functionalisation of the carbosiloxane dendrimers is just as versatile as the above possibility of using different core units. Thus various metallo-carbosilox-ane dendrimers can be constructed, for example with titanocene dichloride end groups [93], ferrocene [94], or dicobalthexacarbonyl units [95]. 

Fig. 4.48 Carbosiloxane dendrimer with terminal Si-H groups (according to Lang et al.)...

Like monodisperse carbosiloxane dendrimers, hyperbranched carbosiloxanes can be produced by hydrosilylation [100]. The first compounds of this kind were synthesised in 1991 by Mathias and Carothers [101] by polymerisation of an al-lyl-tris(dimethylsiloxy)silane monomer with addition of chloroplatinic acid hydrate (Fig. 4.52). The reaction proceeds relatively fast however, addition of more catalyst does not increase the molecular masses (19000 g/mol). The NMR spec-... 

The utilization of allyl alcohol as the nucleophilic reagent to prepare dendritic carbo-siloxanes was also reported by Lang and Brilning134,135. Using a second generation allyl-terminated carbosiloxane dendrimer, they were able to attach titanium moieties via a simple hydrosilylation reaction (equation 12)134. Lang and coworkers were also successful in binding cobalt moieties to ethynyl-terminated carbosiloxane dendrimers (e.g. equation 13)136,137. 

FIGURE 18. Carbosiloxane dendrimer with a pyrene core... 

FIGURE 19. Methyl-terminated carbosiloxane dendrimer synthesized by Sheiko81... 

FIGURE 27.17 UV-vis spectra of carbosilane and carbosiloxane dendrimers in DMSO. 

Less usual carbosilane dendrimers were synthesised by reaction of acetyl-protected hydroxyethyl glycosides with chlorosilanes. Introduction of the carbohydrate component proceeds via alcoholysis of the chlorosilane with formation of silicon-oxygen bonds a carbosilane core unit is formed with carbosiloxane side arms [82]. Reverse assembly of carbosilanes with a carbohydrate core is also feasible [54]. 

The Si-O-C sequence is the distinctive structural unit of carbosilanes. Like that of the carbosilanes, the scaffold of this dendrimer family can be constructed in a targeted manner by the choice of certain core units [88] (Table 4.4). Synthesis of carbosiloxanes generally proceeds by... 

Kim and Kwon reported the divergent synthesis of a dendritic carbosiloxane from a cyclic siloxane tetramer core130 using the standard carbosilane dendrimer synthetic approach. Allyl alcohol was employed as the nucleophilic reagent and trichlorosilane... 

Several dendrimers containing heteroatoms have been well studied, especially Si- and P-based. The Si-based dendrimers were the first to contain second-row heteroatoms and can be classified into polysilanes (Si-Si), carbosilanes (Si-C), carbosiloxanes (Si-O-C), siloxanes (Si-O-Si),... 

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